package org.apache.lucene.search.spans;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.*;
import org.apache.lucene.search.Explanation.IDFExplanation;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;

/**
 * Expert-only.  Public for use by other weight implementations
 */
public class SpanWeight extends Weight {
    protected Similarity similarity;
    protected float value;
    protected float idf;
    protected float queryNorm;
    protected float queryWeight;

    protected Set<Term> terms;
    protected SpanQuery query;
    private IDFExplanation idfExp;

    public SpanWeight(SpanQuery query, Searcher searcher) throws IOException {
        this.similarity = query.getSimilarity(searcher);
        this.query = query;

        terms = new HashSet<Term>();
        query.extractTerms(terms);

        idfExp = similarity.idfExplain(terms, searcher);
        idf = idfExp.getIdf();
    }

    @Override
    public Query getQuery() {
        return query;
    }

    @Override
    public float getValue() {
        return value;
    }

    @Override
    public float sumOfSquaredWeights() throws IOException {
        queryWeight = idf * query.getBoost(); // compute query weight
        return queryWeight * queryWeight; // square it
    }

    @Override
    public void normalize(float queryNorm) {
        this.queryNorm = queryNorm;
        queryWeight *= queryNorm; // normalize query weight
        value = queryWeight * idf; // idf for document
    }

    @Override
    public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
        return new SpanScorer(query.getSpans(reader), this, similarity, reader.norms(query.getField()));
    }

    @Override
    public Explanation explain(IndexReader reader, int doc) throws IOException {

        ComplexExplanation result = new ComplexExplanation();
        result.setDescription("weight(" + getQuery() + " in " + doc + "), product of:");
        String field = ((SpanQuery) getQuery()).getField();

        Explanation idfExpl = new Explanation(idf, "idf(" + field + ": " + idfExp.explain() + ")");

        // explain query weight
        Explanation queryExpl = new Explanation();
        queryExpl.setDescription("queryWeight(" + getQuery() + "), product of:");

        Explanation boostExpl = new Explanation(getQuery().getBoost(), "boost");
        if (getQuery().getBoost() != 1.0f)
            queryExpl.addDetail(boostExpl);
        queryExpl.addDetail(idfExpl);

        Explanation queryNormExpl = new Explanation(queryNorm, "queryNorm");
        queryExpl.addDetail(queryNormExpl);

        queryExpl.setValue(boostExpl.getValue() * idfExpl.getValue() * queryNormExpl.getValue());

        result.addDetail(queryExpl);

        // explain field weight
        ComplexExplanation fieldExpl = new ComplexExplanation();
        fieldExpl.setDescription("fieldWeight(" + field + ":" + query.toString(field) + " in " + doc + "), product of:");

        Explanation tfExpl = ((SpanScorer) scorer(reader, true, false)).explain(doc);
        fieldExpl.addDetail(tfExpl);
        fieldExpl.addDetail(idfExpl);

        Explanation fieldNormExpl = new Explanation();
        byte[] fieldNorms = reader.norms(field);
        float fieldNorm = fieldNorms != null ? similarity.decodeNormValue(fieldNorms[doc]) : 1.0f;
        fieldNormExpl.setValue(fieldNorm);
        fieldNormExpl.setDescription("fieldNorm(field=" + field + ", doc=" + doc + ")");
        fieldExpl.addDetail(fieldNormExpl);

        fieldExpl.setMatch(Boolean.valueOf(tfExpl.isMatch()));
        fieldExpl.setValue(tfExpl.getValue() * idfExpl.getValue() * fieldNormExpl.getValue());

        result.addDetail(fieldExpl);
        result.setMatch(fieldExpl.getMatch());

        // combine them
        result.setValue(queryExpl.getValue() * fieldExpl.getValue());

        if (queryExpl.getValue() == 1.0f)
            return fieldExpl;

        return result;
    }
}
